(1) Field of Invention
This invention relates to stabilization of non-aqueous liquid suspensions, especially non-aqueous liquid fabric-treating compositions. More particularly, this invention relates to non-aqueous liquid laundry detergent compositions which are made stable against phase separation under both static and dynamic conditions and are easily pourable, to the method of preparing these compositions and to the use of these compositions for cleaning soiled fabrics.
(2) Discussion of Prior Art
Liquid nonaqueous heavy duty laundry detergent compositions are well known in the art. For instance, compositions of this type may comprise a liquid nonionic surfactant in which are dispersed particles of a builder, as shown for instance in U.S. Pat. Nos. 4,316,812; 3,630,929; 4,254,466; and 4,661,280.
Liquid detergents are often considered to be more convenient to employ than dry powdered or particulate products and, therefore, have found substantial favor with consumers. They are readily measurable, speedily dissolved in the wash water, capable of being easily applied in concentrated solutions or dispersions to soiled areas on garments to be laundered and are non-dusting, and they usually occupy less storage space. Additionally, the liquid detergents may have incorporated in their formulations materials which could not stand drying operations without deterioration, which materials are often desirably employed in the manufacture of particulate detergent products.
Although they are possessed of many advantages over unitary or particulate solid products, liquid detergents often have certain inherent disadvantages too, which have to be overcome to produce acceptable commercial detergent products. Thus, some such products separate out on storage and others separate out on cooling and are not readily redispersed. In some cases the product viscosity changes and it becomes either too thick to pour or so thin as to appear watery. Some clear products become cloudy and others gel on standing.
The present inventors have been extensively involved as part of an overall corporate research effort in studying the rheological behavior of nonionic liquid surfactant systems with particulate matter suspended therein. Of particular interest have been non-aqueous, built, liquid laundry detergent compositions and the problems of phase separation and settling of the suspended builder and other laundry additives. These considerations have an impact on, for example, product pourability, dispersibility and stability.
It is known that one of the major problems with built, liquid laundry detergents is their physical stability. This problem stems from the fact that the density of the solid suspended particles is higher than the density of the liquid matrix. Therefore, the particles tend to sediment according to Stoke's law. Two basic solutions exist to solve the sedimentation problem: increasing liquid matrix viscosity and/or reducing solid particle size.
For instance, it is known that such suspensions can be stabilized against settling by adding inorganic or organic thickening agents or dispersants, such as, for example, very high surface area inorganic materials, e.g. finely divided silica, clays, etc., organic thickeners, such as the cellulose ethers, acrylic and acrylamide polymers, polyelectrolytes, etc. However, such increases in suspension viscosity are naturally limited by the requirement that the liquid suspension be readily pourable and flowable, even at low temperature. Furthermore, these additives do not contribute to the cleaning performance of the formulation. U.S. Pat. No. 4,661,280 to T. Ouhadi, et al. discloses the use of aluminum stearate for increasing stability of suspensions of builder salts in liquid nonionic surfactant. The addition of small amounts of aluminum stearate increases yield stress without increasing plastic viscosity.
According to U.S. Pat. No. 3,985,668 to W. L. Hartman, an aqueous false body fluid abrasive scouring composition is prepared from an aqueous liquid and an appropriate colloid-forming material, such as clay or other inorganic or organic thickening or suspending agent, especially smectite clays, and a relatively light, water-insoluble particulate filler material, which, like the abrasive material, is suspended throughout the false body fluid phase. The lightweight filler has particle size diameters ranging from 1 to 250 microns and a specific gravity less than that of the false body fluid phase. It is suggested by Hartman that inclusion of the relatively light, insoluble filler in the false body fluid phase helps to minimize phase separation, i.e. minimize formation of a clear liquid layer above the false body abrasive composition, first, by virtue of its buoyancy exerting an upward force on the structure of the colloid-forming agent in the false body phase counteracting the tendency of the heavy abrasive to compress the false body structure and squeeze out liquid. Second, the filler material acts as a bulking agent replacing a portion of the water which would normally be used in the absence of the filler material, thereby resulting in less aqueous liquid available to cause clear layer formation and separation.
British Application GB 2,168,377A, published June 18, 1986, discloses aqueous liquid dishwashing detergent compositions with abrasive, colloidal clay thickener and low density particulate filler having particle sizes ranging from about 1 to about 250 microns and densities ranging from about 0.01 to about 0.5 g/cc, used at a level of from about 0.07% to about 1% by weight of the composition. It is suggested that the filler material improves stability by lowering the specific gravity of the clay mass so that it floats in the liquid phase of the composition. The type and amount of filler is selected such that the specific gravity of the final composition is adjusted to match that of the clear fluid (i.e. the composition without clay or abrasive materials). According to this patent the filler material improves stability by lowering the specific gravity of the clay mass so that it floats in the aqueous liquid phase.
It is also known to include an inorganic insoluble thickening agent or dispersant of very high surface area such as finely divided silica of extremely fine particle size (e.g. of 5-100 millimicrons diameter such as sold under the name Aerosil) or the other highly voluminous inorganic carrier materials as disclosed in U.S. Pat. No. 3,630,929.
It has long been known that aqueous swelling colloidal clays, such as bentonite and montmorillonite clays, can be modified by exchange of the metallic cation groups with organic groups, thereby changing the hydrophilic clays to organophilic clays. The use of such organophilic clays as gel-forming clays has been described in U.S. Pat. 2,531,427 to E. A. Hauser. Improvements and modifications of the organophilic gel-forming clays are described, for example, in the following U.S. Pat. Nos. No. 2,966,506 - Jordan; 4,105,578 - Finlayson, et al.; 4,208,218 Finlayson; 4,287,086 - Finlayson; 4,434,075 - Mardis, et al.; 4,434,076 - Mardis, et al.; all assigned to NL Industries, Inc., formerly National Lead Company. According to these NL patents, these organophilic clay gellants are useful in lubricating greases, oil based muds, oil base packer fluids, paints, paint-varnish-lacquer removers, adhesives, sealants, inks, polyester gel coats and the like. However, use as a stabilizer in a non-aqueous liquid detergent composition for laundering fabrics has not been suggested.
On the other hand, the use of clays in combination with quaternary ammonium compounds (often referred to as "QA" compounds) to impart fabric softening benefits to laundering compositions has been described.. For instance, mention can be made of the British Patent Application GB 2,141,152 A, published Dec. 12, 1984, to P. Ramachandran, and the many patents referred to therein for fabric softening compositions based on organophilic QA clays.
According to the aforementioned U.S. Pat. No. 4,264,466 to Carleton, et al., the physical stability of a dispersion of particulate materials, such as detergent builders, in a non-aqueous liquid phase is improved by using as a primary suspending agent an impalpable chain structure type clay, including sepiolite, attapulgite, and palygorskite clays. The patentees state and the comparative examples in this patent show that other types of clays, such as montmorillonite clay, e.g. Bentolite L, hectorite clay (e.g. Veegum T) and kaolinite clay (e.g., Hydrite PX), even when used in conjunction with an auxiliary suspension aid, including cationic surfactants, inclusive of QA compounds, are only poor suspending agents. Carleton, et al. also refer to use of other clays as suspension aids and mention, as examples, U.S. Pat. Nos. 4,049,034 and 4,005,027 (both aqueous systems); and U.S. Pats. 4,166,039; 3,259,574; 3,557,037 and 3,549,542; and U.K. Patent Application No. 2,017,072.
Commonly assigned copending application Ser. No. 063,199, filed June 12, 1987 (Atty's Docket IR-347LG) discloses incorporation into non-aqueous liquid fabric treating compositions of up to about 1% by weight of an organophilic water-swellable smectite clay modified with a cationic nitrogen-containing compound including at least one long chain hydrocarbon having from about 8 to about 22 carbon atoms to form an elastic network or structure throughout the suspension to increase the yield stress and increase stability of the suspension.
While the addition of the organophilic clay improves stability of the suspension, still further improvements are desired, especially for particulate suspensions having relatively low yield values for optimizing dispensing and dispersion during use.
Grinding to reduce the particle size as a means to increase product stability provides the following advantages:
(1) the particle specific surface area is increased, and, therefore, particle wetting by the non-aqueous vehicle (liquid non-ionic) is proportionately improved; and
(2) the average distance between pigment particles is reduced with a proportionate increase in particle-to-particle interaction.
Each of these effects contributes to increase the rest-gel strength and the suspension yield stress while at the same time,, grinding significantly reduces plastic viscosity.
The above-mentioned U.S. Pat. No. 4,316,812 discloses the benefits of grinding solid particles, e.g., builder and bleach, to an average particle diameter of less than 10 microns. However, it has been found that merely grinding to such small particle sizes does not, by itself, impart sufficient long term stability against phase separation.
In the commonly assigned copending application filed on July 15, 1987 in the names of N. Dixit, et al. under Ser. No. 073,653 (Attorney's Docket IR-4494), and titled "STABLE NON-AQUEOUS CLEANING COMPOSITION CONTAINING LOW DENSITY FILLER AND METHOD OF USE" the use of low density filler material for stabilizing suspensions of finely divided solid particulate matter in a liquid phase against phase separation by equalizing the densities of the dispersed particle phase and the liquid phase is disclosed. These modified liquid suspensions exhibit excellent phase stabilization when left to stand for extended periods of time, e.g., up to 6 months or longer or even when subjected to moderate shaking. However, it has recently been observed that when the low-density filler modified suspensions are subjected to strong vibrations, such as may be encountered during transportation by rail, truck, etc., the homogeneity of the dispersion is degraded as a portion of the low density filler migrates to the upper surface of the liquid suspension.
In commonly assigned, copending application Ser. No. 073,551, filed July 15, 1987 in the name of Cao et al. (Attorney's Docket No. IR-344LG) entitled "Stable Non-Aqueous Suspension Containing Organophilic Clay And Low Density Filler" the use of low density filler material for stabilizing suspensions of finely divided solid particulate matter in a liquid phase against phase separation is disclosed as being improved by the incorporation of organophilic modified clays which aid in resisting the destabilizing effect of strong vibrations.
Nonetheless, still further improvements are desired in the stability of non-aqueous liquid fabric treating compositions.